Re: [PATCH v6 5/8] iommu: Add bounce page APIs

[Lu Baolu]

Hi Joerg,

On 8/15/19 11:48 PM, Joerg Roedel wrote:
> On Thu, Aug 15, 2019 at 02:15:32PM +0800, Lu Baolu wrote:
> > iommu_map/unmap() APIs haven't parameters for dma direction and
> > attributions. These parameters are elementary for DMA APIs. Say,
> > after map, if the dma direction is TO_DEVICE and a bounce buffer is
> > used, we must sync the data from the original dma buffer to the bounce
> > buffer; In the opposite direction, if dma is FROM_DEVICE, before unmap,
> > we need to sync the data from the bounce buffer onto the original
> > buffer.
>
> The DMA direction from DMA-API maps to the protections in iommu_map():
>
> 	DMA_FROM_DEVICE:	IOMMU_WRITE
> 	DMA_TO_DEVICE:		IOMMU_READ
> 	DMA_BIDIRECTIONAL	IOMMU_READ | IOMMU_WRITE
>
> And for the sync DMA-API also has separate functions for either
> direction. So I don't see why these extra functions are needed in the
> IOMMU-API.

Okay. I understand that adding these APIs in iommu.c is not a good idea.
And, I also don't think merging the bounce buffer implementation into
iommu_map() is feasible since iommu_map() is not DMA API centric.

The bounce buffer implementation will eventually be part of DMA APIs
defined in dma-iommu.c, but currently those APIs are not ready for x86
use yet. So I will put them in iommu/vt-d driver for this time being and
will move them to dma-iommu.c later.

Does this work for you?

Best regards,
Lu Baolu